Golf ball

ABSTRACT

An object of the present invention is to provide a golf ball having excellent shot feeling and resilience as well as improved durability and abrasion resistance. The present invention provides a golf ball comprising a spherical core and one or more cover layers disposed outside the spherical core, wherein at least one layer of the cover layers contains: (A) a base resin containing (a-1) an ionomer resin and having a material hardness of 58 or less in Shore D hardness; and (B) a polyrotaxane having a cyclodextrin with at least a part of hydroxyl groups thereof being modified with a caprolactone chain via —O—C 3 H 6 —O— group, a linear molecule piercing through a cyclic structure of the cyclodextrin, and blocking groups located at both terminals of the linear molecule to prevent disassociation of the cyclodextrin.

FIELD OF THE INVENTION

The present invention relates to a technology for improving a cover of agolf ball.

DESCRIPTION OF THE RELATED ART

As a resin component constituting a cover or intermediate layer of agolf ball, a thermoplastic resin such as an ionomer resin or apolyurethane is used. The ionomer resin is highly rigid, and when usedas a constituent member of a golf ball, the resultant golf ball ishighly resilient and travels a great flight distance. Thus, the ionomerresin is widely used as a material of an intermediate layer or coverconstituting a golf ball.

For a golf ball, not only the flight performance, but also variousperformances such as the durability, abrasion resistance and shotfeeling are also desired. For example, as an invention aiming to providea golf ball striking a good balance between the durability and theflight performance, Japanese Patent Publication No. 2011-92708 Adiscloses a golf ball comprising a core, at least one intermediate layerand a cover, wherein the intermediate layer is formed primarily of ahighly neutralized ionomer resin composition having an increasedneutralization degree and obtained by adding a basic inorganic metalcompound or the like in a conventional ionomer resin, and the cover isformed primarily of a mixture comprising an ionomer resin an a granularinorganic filler (refer to claim 1 and paragraphs 0010-0012 in JapanesePatent Publication No. 2011-92708 A).

SUMMARY OF THE INVENTION

Examples of the method for improving the shot feeling of a golf ballinclude a method of lowering the material hardness of the cover toobtain a softer shot feeling. However, although the cover containing aternary ionomer resin has a low material hardness, the golf ballexhibits lowered resilience. In addition, although the cover containinga thermoplastic styrene elastomer has a low material hardness and thegolf ball does not exhibit lowered resilience, the golf ball exhibitsworsened durability and abrasion resistance. Thus, if the materialhardness of the cover is lowered to improve the shot feeling of the golfball, there is a problem that the resilience or the durability andabrasion resistance of the golf ball is worsened.

The present invention has been made in view of the above mentionedcircumstances, and an object of the present invention is to provide agolf ball having excellent shot feeling and resilience as well asimproved durability and abrasion resistance.

The present invention that has solved the above problems provides a golfball comprising a spherical core and one or more cover layers disposedoutside the spherical core, wherein at least one layer of the coverlayers contains: (A) a base resin containing (a-1) an ionomer resin andhaving a material hardness of 58 or less in Shore D hardness; and (B) apolyrotaxane having a cyclodextrin with at least a part of hydroxylgroups of the cyclodextrin being modified with a caprolactone chain via—O—C₃H₆—O— group, a linear molecule piercing through a cyclic structureof the cyclodextrin, and blocking groups located at both terminals ofthe linear molecule to prevent disassociation of the cyclodextrin.

The present invention also provides a golf ball comprising a sphericalcore and one or more cover layers disposed outside the spherical core,wherein at least one layer of the cover layers contains: (A) a baseresin having a material hardness of 58 or less in Shore D hardness andcontaining (a-1) an ionomer resin and (a-2) a non-ionomer resin in amass ratio ((a-2)/(a-1)) of (a-2) the non-ionomer resin to (a-1) theionomer resin ranging from 1/99 to 50/50; and (B) a polyrotaxane havinga cyclodextrin with at least a part of hydroxyl groups of thecyclodextrin being modified with a caprolactone chain via —O—C₃H₆—O—group, a linear molecule piercing through a cyclic structure of thecyclodextrin, and blocking groups located at both terminals of thelinear molecule to prevent disassociation of the cyclodextrin, andwherein the cover layer containing (A) the base resin and (B) thepolyrotaxane contains (B) the polyrotaxane in an amount of from 0.1 partby mass to 20 parts by mass with respect to 100 parts by mass of (A) thebase resin.

According to the present invention, a golf ball having excellent shotfeeling and resilience as well as improved durability and abrasionresistance can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustrative drawing illustrating a molecular structure ofone example of the polyrotaxane used in the present invention; and

FIG. 2 is a partially cutaway sectional view showing a golf ballaccording to an embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention provides a golf ball comprising a spherical coreand one or more cover layers disposed outside the spherical core,wherein at least one layer of the cover layers contains: (A) a baseresin containing (a-1) an ionomer resin and having a material hardnessof 58 or less in Shore D hardness; and (B) a polyrotaxane having acyclodextrin with at least a part of hydroxyl groups of the cyclodextrinbeing modified with a caprolactone chain via —O—C₃H₆—O— group, a linearmolecule piercing through a cyclic structure of the cyclodextrin, andblocking groups located at both terminals of the linear molecule toprevent disassociation of the cyclodextrin. It is noted that anoutermost layer of the cover layers is an outermost layer of a golf ballbody (excluding a paint film).

At least one layer of the cover layers of the golf ball according to thepresent invention is preferably formed from a cover compositioncontaining (A) the base resin and (B) the polyrotaxane as a resincomponent. First, (A) the base resin used in the cover layer of the golfball according to the present invention will be explained.

[(A) Base Resin]

(A) The base resin contains (a-1) the ionomer resin as an essentialcomponent. Examples of (a-1) the ionomer resin include an ionomer resinconsisting of a metal ion-neutralized product of a binary copolymercomposed of an olefin and an α,β-unsaturated carboxylic acid having 3 to8 carbon atoms; an ionomer resin consisting of a metal ion-neutralizedproduct of a ternary copolymer composed of an olefin, an α,β-unsaturatedcarboxylic acid having 3 to 8 carbon atoms and an α,β-unsaturatedcarboxylic acid ester; and a mixture thereof.

It is noted that, in the present invention, “an ionomer resin consistingof a metal ion-neutralized product of a binary copolymer composed of anolefin and an α,β-unsaturated carboxylic acid having 3 to 8 carbonatoms” is sometimes simply referred to as “a binary ionomer resin”, and“an ionomer resin consisting of a metal ion-neutralized product of aternary copolymer composed of an olefin, an α,β-unsaturated carboxylicacid having 3 to 8 carbon atoms and an α,β-unsaturated carboxylic acidester” is sometimes simply referred to as “a ternary ionomer resin”.

The olefin is preferably an olefin having 2 to 8 carbon atoms. Examplesof the olefin include ethylene, propylene, butene, pentene, hexene,heptene and octene, and ethylene is particularly preferred. Examples ofthe α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms includeacrylic acid, methacrylic acid, fumaric acid, maleic acid and crotonicacid, and acrylic acid or methacrylic acid is particularly preferred. Inaddition, examples of the α,β-unsaturated carboxylic acid ester includemethyl ester, ethyl ester, propyl ester, n-butyl ester, isobutyl esterof acrylic acid, methacrylic acid, fumaric acid and maleic acid, andacrylic acid ester or methacrylic acid ester is particularly preferred.

As the binary ionomer resin, a metal ion-neutralized product of anethylene-(meth)acrylic acid binary copolymer is preferable. As theternary ionomer resin, a metal ion-neutralized product of a ternarycopolymer composed of ethylene, (meth)acrylic acid and (meth)acrylicacid ester is preferable. Herein, (meth)acrylic acid means acrylic acidand/or methacrylic acid.

The amount of the α,β-unsaturated carboxylic acid component having 3 to8 carbon atoms in the binary ionomer resin is preferably 5 mass % ormore, more preferably 10 mass % or more, even more preferably 16 mass %or more, and most preferably 17 mass % or more, and is preferably 30mass % or less, more preferably 25 mass % or less. This is because ifthe amount of the α,β-unsaturated carboxylic acid component having 3 to8 carbon atoms is 5 mass % or more, the constituent member having adesirable hardness is easily obtained, and if the amount of theα,β-unsaturated carboxylic acid component having 3 to 8 carbon atoms is30 mass % or less, the hardness of the obtained constituent member isnot too high and thus the durability and the shot feeling of the golfball are better.

The neutralization degree of the carboxyl groups of the binary ionomerresin is preferably 15 mole % or more, more preferably 20 mole % ormore, and is preferably 90 mole % or less, more preferably 85 mole % orless. If the neutralization degree is 15 mole % or more, the obtainedgolf ball has better resilience and durability, and if theneutralization degree is 90 mole % or less, the cover material hasbetter fluidity (better moldability). It is noted that theneutralization degree of the carboxyl groups of the binary ionomer resinmay be calculated by the following expression.

Neutralization degree of binary ionomer resin (mole %)=100×(mole numberof neutralized carboxyl groups in binary ionomer resin/mole number ofall carboxyl groups in binary ionomer resin)

Examples of the metal ion for neutralizing at least a part of carboxylgroups of the binary ionomer resin include monovalent metal ions such assodium, potassium and lithium; divalent metals ions such as magnesium,calcium, zinc, barium and cadmium; trivalent metals ions such asaluminum; and other ions such as tin and zirconium. As the binaryionomer resin, a mixture consisting of a sodium-neutralized binaryionomer resin and a zinc-neutralized binary ionomer resin is preferablyused. Using the mixture further enhances the resilience and thedurability.

Specific examples of the binary ionomer resin include trade names of“Himilan (registered trademark) (e.g. Himilan 1555 (Na), Himilan 1557(Zn), Himilan 1605 (Na), Himilan 1702 (Zn), Himilan 1706 (Zn), Himilan1707 (Na), Himilan AM7311 (Mg), Himilan AM7329 (Zn), Himilan AM7337(Na))” available from Mitsui-Du Pont Polychemicals Co., Ltd.

Specific examples of the binary ionomer resin further include tradenames of “Surlyn (registered trademark) (e.g. Surlyn 8945 (Na), Surlyn9945 (Zn), Surlyn 8140 (Na), Surlyn 8150 (Na), Surlyn 9120 (Zn), Surlyn9150 (Zn), Surlyn 6910 (Mg), Surlyn 6120 (Mg), Surlyn 7930 (Li), Surlyn7940 (Li), Surlyn AD8546 (Li))” available from E.I. du Pont de Nemoursand Company.

Specific examples of the binary ionomer resin further include tradenames of “Iotek (registered trademark) (e.g. Iotek 8000 (Na), Iotek 8030(Na), Iotek 7010 (Zn), Iotek 7030 (Zn))” available from ExxonMobilChemical Corporation.

The above listed binary ionomer resin may be used solely, or at leasttwo of them may be used in combination. It is noted that Na, Zn, Li, Mgand the like described in the parentheses after the trade names indicatemetal types of neutralizing metal ions of the binary ionomer resins.

The bending stiffness of the binary ionomer resin is preferably 140 MPaor more, more preferably 150 MPa or more, and even more preferably 160MPa or more, and is preferably 550 MPa or less, more preferably 500 MPaor less, and even more preferably 450 MPa or less. If the bendingstiffness falls within the above range, the spin rate on driver shots isoptimized and thus the flight performance is excellent, and thedurability is also better.

The melt flow rate (190° C., 2.16 kgf) of the binary ionomer resin ispreferably 0.1 g/10 min or more, more preferably 0.5 g/10 min or more,and even more preferably 1.0 g/10 min or more, and is preferably 30 g/10min or less, more preferably 20 g/10 min or less, and even morepreferably 15 g/10 min or less. If the melt flow rate (190° C., 2.16kgf) of the binary ionomer resin is 0.1 g/10 min or more, the covermaterial has better fluidity, and thus, for example, a thin cover can beobtained. In addition, if the melt flow rate (190° C., 2.16 kgf) of thebinary ionomer resin is 30 g/10 min or less, the obtained golf ball hasbetter durability.

The amount of the α,β-unsaturated carboxylic acid component having 3 to8 carbon atoms in the ternary ionomer resin is preferably 2 mass % ormore, more preferably 3 mass % or more, and is preferably 30 mass % orless, more preferably 25 mass % or less.

The neutralization degree of the carboxyl groups of the ternary ionomerresin is preferably 20 mole % or more, more preferably 30 mole % ormore, and is preferably 90 mole % or less, more preferably 85 mole % orless. If the neutralization degree is 20 mole % or more, the obtainedgolf ball has better resilience and durability, and if theneutralization degree is 90 mole % or less, the cover material hasbetter fluidity (better moldability). It is noted that theneutralization degree of the carboxyl groups of the ionomer resin may becalculated by the following expression.

Neutralization degree of ionomer resin (mole %)=100×(mole number ofneutralized carboxyl groups in ionomer resin/mole number of all carboxylgroups in ionomer resin)

Examples of the metal ion for neutralizing at least a part of carboxylgroups of the ternary ionomer resin include monovalent metal ions suchas sodium, potassium and lithium; divalent metals ions such asmagnesium, calcium, zinc, barium and cadmium; trivalent metals ions suchas aluminum; and other ions such as tin and zirconium.

Specific examples of the ternary ionomer resin include trade names of“Himilan (registered trademark) (e.g. Himilan AM7327 (Zn), Himilan 1855(Zn), Himilan 1856 (Na), Himilan AM7331 (Na))” available from Mitsui-DuPont Polychemicals Co., Ltd.; trade names of “Surlyn 6320 (Mg), Surlyn8120 (Na), Surlyn 8320 (Na), Surlyn 9320 (Zn), Surlyn 9320W (Zn))”available from E.I. du Pont de Nemours and Company; and trade names of“Iotek 7510 (Zn), Iotek 7520 (Zn))” available from ExxonMobil ChemicalCorporation. It is noted that Na, Zn, Mg and the like described in theparentheses after the trade names indicate metal types of neutralizingmetal ions of the ternary ionomer resins. The ternary ionomer resin maybe used solely, or at least two of them may be used in combination.

The bending stiffness of the ternary ionomer resin is preferably 10 MPaor more, more preferably 11 MPa or more, and even more preferably 12 MPaor more, and is preferably 100 MPa or less, more preferably 97 MPa orless, and even more preferably 95 MPa or less. If the bending stiffnessfalls within the above range, the spin rate on driver shots is optimizedand thus the flight performance is excellent, and the durability is alsobetter.

The melt flow rate (190° C., 2.16 kgf) of the ternary ionomer resin ispreferably 0.1 g/10 min or more, more preferably 0.3 g/10 min or more,and even more preferably 0.5 g/10 min or more, and is preferably 20 g/10min or less, more preferably 15 g/10 min or less, and even morepreferably 10 g/10 min or less. If the melt flow rate (190° C., 2.16kgf) of the ternary ionomer resin is 0.1 g/10 min or more, the covermaterial has better fluidity, and thus, for example, a thin constituentmember can be obtained. In addition, if the melt flow rate (190° C.,2.16 kgf) of the ternary ionomer resin is 20 g/10 min or less, theobtained golf ball has better durability.

The amount of (a-1) the ionomer resin in (A) the resin component ispreferably 50 mass % or more, more preferably 60 mass % or more, andeven more preferably 70 mass % or more. This is because if the amount of(a-1) the ionomer resin is 50 mass % or more, lowering in the resilienceof the obtained golf ball can be suppressed. The upper limit of theabove amount is preferably 100 mass %, without any limitation.

The material hardness of (a-1) the ionomer resin used in the presentinvention is preferably 40 or more, more preferably 43 or more, and evenmore preferably 45 or more in Shore D hardness, and is preferably 65 orless, more preferably 62 or less, and even more preferably 58 or less inShore D hardness. This is because if the material hardness is 40 or morein Shore D hardness, the obtained golf ball has further enhancedresilience, and if the material hardness is 65 or less in Shore Dhardness, the obtained golf ball has further enhanced durability.

(a-1) The ionomer resin used in the present invention may be prepared byneutralizing a binary copolymer composed of an olefin and anα,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and/or aternary copolymer composed of an olefin, an α,β-unsaturated carboxylicacid having 3 to 8 carbon atoms and an α,β-unsaturated carboxylic acidester with a metal compound when molding the cover.

The olefin is preferably an olefin having 2 to 8 carbon atoms. Examplesof the olefin include ethylene, propylene, butene, pentene, hexene,heptene and octene, and ethylene is particularly preferred. Examples ofthe α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms includeacrylic acid, methacrylic acid, fumaric acid, maleic acid and crotonicacid, and acrylic acid or methacrylic acid is particularly preferred. Inaddition, examples of the α,β-unsaturated carboxylic acid ester includemethyl ester, ethyl ester, propyl ester, n-butyl ester, isobutyl esterof acrylic acid, methacrylic acid, fumaric acid and maleic acid, andacrylic acid ester or methacrylic acid ester is particularly preferred.

Specific examples of the binary copolymer include anethylene-methacrylic acid copolymer having a trade name of “NUCREL(registered trademark) (e.g. “NUCREL N1050H”, “NUCREL N2050H”, “NUCRELN1110H”, “NUCREL N0200H”)” available from Mitsui-Du Pont PolychemicalsCo., Ltd.; and an ethylene-acrylic acid copolymer having a trade name of“PRIMACOR (registered trademark) 5980I” available from Dow ChemicalCompany.

Specific examples of the ternary copolymer include trade names of“NUCREL (registered trademark) (e.g. “NUCREL AN4318”, “NUCREL AN4319”)”available from Mitsui-Du Pont Polychemicals Co., Ltd.; trade names of“NUCREL (registered trademark) (e.g. “NUCREL AE”)” available from E.I.du Pont de Nemours and Company; and trade names of “PRIMACOR (registeredtrademark) (e.g. “PRIMACOR AT310”, “PRIMACOR AT320”)” available from DowChemical Company. The binary copolymer or ternary copolymer may be usedsolely, or at least two of them may be used in combination.

Examples of the metal compound for neutralizing the carboxyl groups ofthe binary copolymer and/or the ternary copolymer include a metalhydroxide such as magnesium hydroxide, zinc hydroxide, calciumhydroxide, sodium hydroxide, lithium hydroxide, potassium hydroxide, andcopper hydroxide; a metal oxide such as magnesium oxide, calcium oxide,zinc oxide, and copper oxide; and a metal carbonate such as magnesiumcarbonate, zinc carbonate, calcium carbonate, sodium carbonate, lithiumcarbonate, and potassium carbonate.

(A) The base resin may further contain a resin component (hereinafter,sometime referred to as “(a-2) a non-ionomer resin”) other than theionomer resin. Examples of (a-2) the non-ionomer resin include athermoplastic resin such as polyamide and polyolefin; a thermoplasticelastomer such as styrene elastomer, polyolefin elastomer, polyamideelastomer and polyester elastomer; a binary copolymer composed of anolefin and an α,β-unsaturated carboxylic acid having 3 to 8 carbon atomssuch as ethylene-(meth)acrylic acid copolymer; and a ternary copolymercomposed of an olefin, an α,β-unsaturated carboxylic acid having 3 to 8carbon atoms and an α,β-unsaturated carboxylic acid ester such asethylene-(meth)acrylic acid-(meth)acrylic acid ester copolymer. (a-2)The non-ionomer resin may be used solely, or at least two of them may beused in combination. In addition, (A) the base resin may consist of(a-1) the ionomer resin.

(a-2) The non-ionomer resin is preferably at least one member selectedfrom the group consisting of polyamide, styrene elastomer, polyolefinelastomer, polyamide elastomer, polyester elastomer, the binarycopolymer composed of an olefin and an α,β-unsaturated carboxylic acidhaving 3 to 8 carbon atoms, and the ternary copolymer composed of anolefin, an α,β-unsaturated carboxylic acid having 3 to 8 carbon atomsand an α,β-unsaturated carboxylic acid ester.

The polyamide is not particularly limited, as long as it is athermoplastic resin having a plurality of amide bonds (—NH—CO—) in themain chain of the molecule. Examples of the polyamide include a producthaving amide bonds in the molecule, formed by a ring-openingpolymerization reaction of a lactam, or a reaction between a diaminecomponent and a dicarboxylic acid component.

Examples of the polyamide include an aliphatic polyamide such aspolyamide 6, polyamide 11, polyamide 12, polyamide 66, polyamide 610,polyamide 6T, polyamide 6I, polyamide 9T, polyamide M5T and polyamide612; and an aromatic polyamide such as poly-p-phenylene terephthalamideand poly-m-phenylene isophthalamide. These polyamides may be usedsolely, or two or more of them may be used in combination. Among them,the aliphatic polyamide such as polyamide 6, polyamide 66, polyamide 11,and polyamide 12 is preferred.

Specific examples of the polyamide include trade names of “Rilsan(registered trademark) B (e.g. Rilsan BESN TL, Rilsan BESN P20 TL,Rilsan BESN P40 TL, Rilsan MB3610, Rilsan BMF O, Rilsan BMN O, RilsanBMN O TLD, Rilsan BMN BK TLD, Rilsan BMN P20 D, Rilsan BMN P40 D)”available from Arkema Inc.

The polyolefin is not particularly limited, as long as it is a compoundsynthesized by using one or at least two olefins as a monomer. Theolefin is preferably an olefin having 2 to 8 carbon atoms. Examples ofthe olefin include ethylene, propylene, butene, pentene, hexene, hepteneand octane. As the polyolefin, polyethylene and polypropylene arepreferable, polyethylene is more preferable.

As the styrene elastomer, a thermoplastic elastomer containing a styreneblock is preferably used. The thermoplastic elastomer containing thestyrene block includes a polystyrene block as a hard segment, and a softsegment. The typical soft segment is a diene block. Examples of theconstituent component of the diene block include butadiene, isoprene,1,3-pentadiene and 2,3-dimethyl-1,3-butadiene. Among them, butadiene andisoprene are preferred. Two or more constituent components may be usedin combination.

Examples of the thermoplastic elastomer containing the styrene blockinclude a styrene-butadiene-styrene block copolymer (SBS), astyrene-isoprene-styrene block copolymer (SIS), astyrene-isoprene-butadiene-styrene block copolymer (SIBS), ahydrogenated product of SBS, a hydrogenated product of SIS and ahydrogenated product of SIBS. Examples of the hydrogenated product ofSBS include a styrene-ethylene-butylene-styrene block copolymer (SEBS).Examples of the hydrogenated product of SIS include astyrene-ethylene-propylene-styrene block copolymer (SEPS). Examples ofthe hydrogenated product of SIBS include astyrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS).

The amount of the styrene component in the thermoplastic elastomercontaining the styrene block is preferably 10 mass % or more, morepreferably 12 mass % or more, and even more preferably 15 mass % ormore. From the viewpoint of the shot feeling of the obtained golf ball,the above amount is preferably 50 mass % or less, more preferably 47mass % or less, and even more preferably 45 mass % or less.

Examples of the thermoplastic elastomer containing the styrene blockinclude an alloy of one member or at least two members selected from thegroup consisting of SBS, SIS, SIBS, SEBS, SEPS, SEEPS and hydrogenatedproducts thereof with a polyolefin. It is estimated that the olefincomponent in the alloy contributes to the improvement in compatibilitywith the ionomer resin. If the alloy is used, the resilience performanceof the golf ball is enhanced. An olefin having 2 to 10 carbon atoms ispreferably used. Suitable olefins include ethylene, propylene, butaneand pentene. Ethylene and propylene are particularly preferred.

Specific examples of the alloy include “Rabalon (registered trademark)T3221C”, “Rabalon T3339C”, “Rabalon SJ4400N”, “Rabalon SJ5400N”,“Rabalon SJ6400N”, “Rabalon SJ7400N”, “Rabalon SJ8400N”, “RabalonSJ9400N” and “Rabalon SR04” available from Mitsubishi ChemicalCorporation. Specific examples of the other thermoplastic elastomercontaining the styrene block include “Epofriend A1010” available fromDaicel Chemical Industries, Ltd., and “Septon HG-252” available fromKuraray Co., Ltd.

As the polyolefin elastomer, a polyolefin elastomer containing ethyleneas a constituent component is preferable. Examples of the thermoplasticpolyolefin elastomer containing a functional group includeethylene-glycidyl (meth)acrylate copolymer, ethylene-(meth)acrylic acidester-glycidyl (meth)acrylate copolymer, ethylene-glycidyl(meth)acrylate-vinyl acetate copolymer.

The polyamide elastomer has a hard segment derived from a polyamidecomponent, and a soft segment. Examples of the component constitutingthe soft segment of the polyamide elastomer include a polyether estercomponent and a polyether component. Examples of the polyamide elastomerinclude a polyether ester amide obtained by a reaction between apolyamide component (hard segment component) and a polyether estercomponent (soft segment component) which is formed from apolyoxyalkylene glycol and a dicarboxylic acid; and a polyether amideobtained by a reaction between a polyamide component (hard segmentcomponent) and a polyether component (soft segment component) which isformed from a dicarboxylic acid or diamine and a compound obtained byaminating or carboxylating both terminals of a polyoxyalkylene glycol.

Examples of the polyamide elastomer include “Pebax 2533”, “Pebax 3533”,“Pebax 4033”, “Pebax 5533” available from Arkema K. K.

Examples of the polyester elastomer include a block copolymer having ahard segment derived from a polyester component, and a soft segment.Examples of the polyester component constituting the hard segmentinclude an aromatic polyester. Examples of the component constitutingthe soft segment include an aliphatic polyether and an aliphaticpolyester.

Specific examples of the polyester elastomer include “Hytrel 3548”,“Hytrel 4047” available from Du Pont-Toray Co., Ltd., and “PrimalloyA1606”, “Primalloy B1600”, “Primalloy B1700” available from MitsubishiChemical Corporation.

Specific examples of the ethylene-(meth)acrylic acid copolymer includean ethylene-methacrylic acid copolymer having a trade name of “NUCREL(registered trademark) (e.g. “NUCREL N1050H”, “NUCREL N2050H”, “NUCRELN1110H”, “NUCREL N0200H”)” available from Mitsui-Du Pont PolychemicalsCo., Ltd.; and an ethylene-acrylic acid copolymer having a trade name of“PRIMACOR (registered trademark) 5980I” available from Dow ChemicalCompany.

Specific examples of the ethylene-(meth)acrylic acid-(meth)acrylic acidester copolymer include trade names of “NUCREL (registered trademark)(e.g. “NUCREL AN4318”, “NUCREL AN4319”)” available from Mitsui-Du PontPolychemicals Co., Ltd.; trade names of “NUCREL (registered trademark)(e.g. “NUCREL AE”)” available from E.I. du Pont de Nemours and Company;and trade names of “PRIMACOR (registered trademark) (e.g. “PRIMACORAT310”, “PRIMACOR AT320”)” available from Dow Chemical Company).

In the case that (A) the base resin contains (a-2) the non-ionomerresin, the amount of (a-2) the non-ionomer resin in (A) the base resinis preferably 1 mass % or more, more preferably 3 mass % or more, andeven more preferably 5 mass % or more, and is preferably 50 mass % orless, more preferably 40 mass % or less, and even more preferably 30mass % or less. This is because if the amount of (a-2) the non-ionomerresin is 1 mass % or more, the obtained golf ball has better shotfeeling, and if the amount of (a-2) the non-ionomer resin is 50 mass %or less, lowering in the durability of the obtained golf ball can besuppressed.

In the case that (A) the base resin contains (a-2) the non-ionomerresin, the mass ratio ((a-2)/(a-1)) of the amount of (a-2) thenon-ionomer resin to the amount of (a-1) the ionomer resin in (A) thebase resin is preferably 1/99 or more, more preferably 3/97 or more, andeven more preferably 5/95 or more, and is preferably 50/50 or less, morepreferably 40/60 or less, and even more preferably 30/70 or less.

The material hardness of (A) the base resin used in the presentinvention is preferably 42 or more, more preferably 45 or more, and evenmore preferably 48 or more in Shore D hardness, and is preferably 58 orless, more preferably 57 or less, and even more preferably 56 or less inShore D hardness. If the material hardness of (A) the base resin is 42or more in Shore D hardness, the obtained golf ball has further enhancedresilience. In addition, if the material hardness of (A) the base resinis 58 or less in Shore D hardness, lowering in the durability due torepeated hitting can be further suppressed. It is noted that thematerial hardness of the base resin is a slab hardness obtained bymeasuring a sheet molded from the base resin.

[(B) Polyrotaxane]

Next, (B) the polyrotaxane used in the present invention will beexplained. (B) The polyrotaxane has a cyclodextrin, a linear moleculepiercing through a cyclic structure of the cyclodextrin, and blockinggroups located at both terminals of the linear molecule to preventdisassociation of the cyclodextrin. The polyrotaxane is viscoelastic,since the cyclodextrin molecule is movable along the linear moleculethat penetrates the cyclodextrin in a skewering manner (pulley effect).Even if a tension is applied to the polyrotaxane, the tension can beuniformly dispersed due to the pulley effect.

The cyclodextrin is a general term for an oligosaccharide having acyclic structure. The cyclodextrin is, for example, a molecule having 6to 8 D-glucopyranose residues being linked in a cyclic shape via anα-1,4-glucoside bond. Examples of the cyclodextrin includea-cyclodextrin (number of glucose units: 6), β-cyclodextrin (number ofglucose units: 7), and γ-cyclodextrin (number of glucose units: 8), andthe α-cyclodextrin is preferable. As the cyclodextrin, one type may beused solely, and two or more types may be used in combination.

The linear molecule is not particularly limited, as long as it is alinear molecule capable of piercing through the cyclic structure of thecyclodextrin so that the cyclic structure of the cyclodextrin isrotatable around the linear molecule. Examples of the linear moleculeinclude polyalkylene, polyester, polyether, and polyacrylic acid. Amongthem, the polyether is preferable, and polyethylene glycol isparticularly preferable. The polyethylene glycol has less sterichindrance, and thus can easily pierce through the cyclic structure ofthe cyclodextrin.

The weight average molecular weight of the linear molecule is preferably5,000 or more, more preferably 6,000 or more, and is preferably 100,000or less, more preferably 80,000 or less.

The linear molecule preferably has a functional group at both terminalsthereof. When the linear molecule has the functional group, the linearmolecule can easily react with the blocking group. Examples of thefunctional group include a hydroxyl group, carboxyl group, amino group,and thiol group.

The blocking group is not particularly limited, as long as it is locatedat both terminals of the linear molecule to prevent the cyclodextrinfrom disassociating from the linear molecule. Examples of the method forpreventing the disassociation include a method of using a bulky blockinggroup to physically prevent the disassociation, and a method of using anionic blocking group to electrostatically prevent the disassociation.Examples of the bulky blocking group include a cyclodextrin and anadamantyl group. The number of the cyclodextrins which the linearmolecule pierces through preferably ranges from 0.06 to 0.61, morepreferably ranges from 0.11 to 0.48, and even more preferably rangesfrom 0.24 to 0.41, if the maximum number of the cyclodextrins which thelinear molecule pierces through is deemed as 1. This is because if thenumber of the cyclodextrins which the linear molecule pierces through isless than 0.06, the pulley effect may not be exerted, and if the numberof the cyclodextrins which the linear molecule pierces through exceeds0.61, the cyclodextrins are so densely located that the movability ofthe cyclodextrin may decrease.

As (B) the polyrotaxane having the cyclodextrin used in the presentinvention, it is preferable that at least a part of hydroxyl groups ofthe cyclodextrin is modified with a caprolactone chain. This is becausemodifying with the caprolactone enhances the flexibility of the coverlayer, thereby achieving better shot feeling.

As the above modification, for example, the hydroxyl groups of thecyclodextrin are treated with propylene oxide to hydroxylpropylate thecyclodextrin, and then E-caprolactone is added to perform ring-openingpolymerization. As a result of this modification, the caprolactone chain—(CO(CH₂)₅O)nH (n is a natural number of from 1 to 100) is linked to theexterior side of the cyclic structure of the cyclodextrin via —O—C₃H₆—O—group. The n represents the degree of polymerization, and is preferablya natural number of from 1 to 100, more preferably a natural number offrom 2 to 70, and even more preferably a natural number of from 3 to 40.At the other end of the caprolactone chain, a hydroxyl group is formedthrough the ring-opening polymerization.

The ratio of the hydroxyl groups modified with the caprolactone chain toall the hydroxyl groups (100 mole %) included in the cyclodextrin beforethe modification is preferably 2 mole % or more, more preferably 5 mole% or more, and even more preferably 10 mole % or more, and is preferably50 mole % or less, more preferably 30 mole % or less, and even morepreferably 20 mole % or less. This is because if the ratio of thehydroxyl groups modified with the caprolactone chain falls within theabove range, the compatibility of the polyrotaxane with the ionomerresin is further enhanced.

FIG. 1 is an illustrative drawing illustrating a molecular structure ofone example of (B) the polyrotaxane used in the present invention. Apolyrotaxane 10 has a cyclodextrin 12, a linear molecule 14 piercingthrough the cyclic structure of the cyclodextrin 12, and blocking groups16 located at both terminals of the linear molecule 14 to preventdisassociation of the cyclodextrin 12, and a caprolactone chain 18 islinked to the exterior side of the cyclic structure of the cyclodextrin12 via —O—C₃H₆—O— group (not shown).

The hydroxyl value of (B) the polyrotaxane is preferably 10 mg KOH/g ormore, more preferably 15 mg KOH/g or more, and even more preferably 20mg KOH/g or more, and is preferably 400 mg KOH/g or less, morepreferably 300 mg KOH/g or less, even more preferably 220 mg KOH/g orless, and particularly preferably 180 mg KOH/g or less. This is becauseif the hydroxyl value of (B) the polyrotaxane falls within the aboverange, the compatibility of (B) the polyrotaxane with the ionomer resinis further enhanced. It is noted that the hydroxyl value may be measuredaccording to JIS K 1557-1, for example, by an acetylation method.

The total molecular weight of (B) the polyrotaxane is preferably 30,000or more, more preferably 40,000 or more, and even more preferably 50,000or more, and is preferably 3,000,000 or less, more preferably 2,500,000or less, and even more preferably 2,000,000 or less, in a weight averagemolecular weight. This is because if the weight average molecular weightis 30,000 or more, the resultant cover composition has greaterelasticity, and if the weight average molecular weight is 3,000,000 orless, the resultant cover composition has greater flexibility and thusthe shot feeling is further enhanced. It is noted that the weightaverage molecular weight may be measured, for example, by gel permeationchromatography (GPC) using polystyrene as a standard substance,tetrahydrofuran as an eluant, and an organic solvent system GPC column(e.g., “Shodex (registered trademark) KF series” available from ShowaDenko K.K.) as a column.

Specific examples of the polyrotaxane modified with the polycaprolactoneinclude SeRM (registered trademark) super polymer SH3400P, SH2400P andSH1310P available from Advanced Softmaterials Inc.

At least one layer of the cover layers of the golf ball according to thepresent invention is formed from the cover composition containing (A)the base resin and (B) the polyrotaxane as the resin component. Thecover layer containing (A) the base resin and (B) the polyrotaxanecontains (B) the polyrotaxane preferably in an amount of 0.1 part bymass or more, more preferably in an amount of 1 part by mass or more,and even more preferably in an amount of 3 parts by mass or more, andpreferably in an amount of 20 parts by mass or less, more preferably inan amount of 15 parts by mass or less, and even more preferably in anamount of 13 parts by mass or less, with respect to 100 parts by mass of(A) the base resin. This is because if the amount of (B) thepolyrotaxane is 0.1 part by mass or more, the obtained golf ballexhibits further enhanced resilience, and if the amount of (B) thepolyrotaxane is 20 parts by mass or less, the mold release propertywould not be affected when molding the golf ball.

In the case that the golf ball according to the present inventioncomprises a plurality of cover layers, at least one layer of the coverlayers contains (A) the base resin and (B) the polyrotaxane, and thelayer not containing (A) the base resin and (B) the polyrotaxane maycontain another resin component. Examples of the other resins include athermoplastic resin such as polyurethane, ionomer resin, polyamide andpolyethylene; and a thermoplastic elastomer such as styrene elastomer,polyolefin elastomer, polyurethane elastomer, polyamide elastomer andpolyester elastomer.

Specific examples of the other resin include an ionomer resin having atrade name of “Himilan (registered trademark)” available from Mitsui-DuPont Polychemicals Co., Ltd., a thermoplastic polyurethane elastomerhaving a trade name of “Elastollan (registered trademark)” availablefrom BASF Japan Ltd., a thermoplastic polyamide elastomer having a tradename of “Pebax (registered trademark)” available from Arkema K. K., athermoplastic polyester elastomer having a trade name of “Hytrel(registered trademark)” available from Du Pont-Toray Co., Ltd., and athermoplastic styrene elastomer having a trade name of “Rabalon(registered trademark)” or a thermoplastic polyester elastomer having atrade name of “Primalloy” available from Mitsubishi ChemicalCorporation.

The total ratio of (A) the base resin and (B) the polyrotaxane to allthe resin components in the cover layer containing (A) the base resinand (B) the polyrotaxane is preferably 60 mass % or more, morepreferably 70 mass % or more, and even more preferably 80 mass % ormore. This is because if the total ratio is 60 mass % or more, theobtained golf ball exhibits further enhanced resilience. The upper limitof the total ratio is preferably 100 mass %, without any limitation.

The cover of the golf ball according to the present invention mayfurther contain a pigment component such as a white pigment (e.g.titanium oxide), a blue pigment and a red pigment, a weight adjustingagent such as calcium carbonate and barium sulfate, a dispersant, anantioxidant, an ultraviolet absorber, a light stabilizer, a fluorescentmaterial or fluorescent brightener, unless they impair the performanceof the cover.

In the present invention, the material hardness of the cover layercontaining (A) the base resin and (B) the polyrotaxane is preferably 40or more, more preferably 42 or more, and even more preferably 45 or morein Shore D hardness, and is preferably 58 or less, more preferably 57 orless, and even more preferably 56 or less in Shore D hardness. This isbecause if the material hardness is 40 or more in Shore D hardness,lowering in the resilience of the obtained golf ball can be suppressed,and if the material hardness is 58 or less in Shore D hardness, theobtained golf ball has better shot feeling. It is noted that thematerial hardness of the cover layer containing (A) the base resin and(B) the polyrotaxane is a slab hardness obtained by measuring a sheetmolded from the cover composition containing (A) the base resin and (B)the polyrotaxane.

The spherical core of the golf ball according to the present inventionis preferably formed from a resin composition or a rubber composition,and more preferably formed from a rubber composition. The spherical coremay be formed, for example, by heat pressing a rubber composition(hereinafter, sometimes simply referred to as “core rubber composition”)containing a base rubber, a co-crosslinking agent, and a crosslinkinginitiator.

As the base rubber, particularly preferred is a high cis-polybutadienehaving a cis-bond which is beneficial to the resilience in an amount of40 mass % or more, preferably 70 mass % or more, and more preferably 90mass % or more. As the co-crosslinking agent, an α,β-unsaturatedcarboxylic acid having 3 to 8 carbon atoms or a metal salt thereof ispreferred, and an acrylic acid metal salt and an methacrylic acid metalsalt are more preferred. As the metal constituting the metal salt, zinc,magnesium, calcium, aluminum and sodium are preferred, and zinc is morepreferred. The amount of the co-crosslinking agent is preferably 15parts by mass or more and 50 parts by mass or less with respect to 100parts by mass of the base rubber. As the crosslinking initiator, anorganic peroxide is preferably used. Specific examples of the organicperoxide include dicumyl peroxide,1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane,2,5-dimethyl-2,5-di(t-butylperoxy) hexane, and di-t-butyl peroxide.Among them, dicumyl peroxide is preferably used. The amount of thecrosslinking initiator is preferably 0.2 part by mass or more, morepreferably 0.3 part by mass or more, and is preferably 3 parts by massor less, more preferably 2 parts by mass or less, with respect to 100parts by mass of the base rubber.

The core rubber composition may further contain an organic sulfurcompound. Examples of the organic sulfur compound include compounds ofdiphenyl disulfides (e.g. diphenyl disulfides, bis(pentabromophenyl)disulfides), thiophenols and thionaphthols. The amount of the organicsulfur compound is preferably 0.01 part by mass or more, more preferably0.05 part by mass or more, and is preferably 5.0 parts by mass or less,more preferably 3.0 parts by mass or less, with respect to 100 parts bymass of the base rubber. The core rubber composition may further containa carboxylic acid and/or a salt thereof. As the carboxylic acid and/orthe salt thereof, a carboxylic acid having 1 to 30 carbon atoms and/or asalt thereof is preferred. As the carboxylic acid, any one of analiphatic carboxylic acid (e.g. caprylic acid) and an aromaticcarboxylic acid (e.g. benzoic acid) may be used. The amount of thecarboxylic acid and/or the salt thereof is 1 part by mass or more and 40parts by mass or less with respect to 100 parts by mass of the baserubber.

The core rubber composition may appropriately contain a weight adjustingagent such as zinc oxide and barium sulfate, an antioxidant, or acolored powder, in addition to the base rubber, the co-crosslinkingagent, the crosslinking initiator, and the organic sulfur compound.

[Construction of Golf Ball]

The construction of the golf ball according to the present invention isnot particularly limited, as long as the golf ball comprises a sphericalcore and one or more cover layers covering the spherical core. Examplesof the construction of the golf ball include a two-piece golf ballcomposed of a single-layered spherical core and a single-layered covercovering the spherical core wherein the single-layered cover contains(A) the base resin and (B) the polyrotaxane; a three-piece golf ballcomposed of a single-layered spherical core, an inner cover layercovering the spherical core and an outer cover layer covering the innercover layer wherein either or both of the inner cover layer and theouter cover layer contains (A) the base resin and (B) the polyrotaxane;a multi-piece golf ball (e.g. a four-piece golf ball, a five-piece golfball) composed of a single-layered spherical core, two or more innercover layers covering the spherical core and an outermost cover layercovering the inner cover layers wherein at least one layer of the two ormore inner cover layers contains (A) the base resin and (B) thepolyrotaxane; and a multi-piece golf ball (e.g. a four-piece golf ball,a five-piece golf ball) composed of a single-layered spherical core, twoor more inner cover layers covering the spherical core and an outermostcover layer covering the inner cover layers wherein the outermost coverlayer contains (A) the base resin and (B) the polyrotaxane.

In the multi-piece golf ball (e.g. four-piece golf ball, five-piece golfball) composed of a single-layered spherical core, two or more innercover layers covering the spherical core and an outermost cover layercovering the inner cover layers wherein at least one layer of the two ormore inner cover layers contains (A) the base resin and (B) thepolyrotaxane, the outermost layer of the inner cover layers preferablycontains (A) the base resin and (B) the polyrotaxane, and all layers ofthe inner cover layers may contain (A) the base resin and (B) thepolyrotaxane.

In the multi-piece golf ball (e.g. four-piece golf ball, five-piece golfball) composed of a single-layered spherical core, two or more innercover layers covering the spherical core and an outermost cover layercovering the inner cover layers wherein the outermost cover layercontains (A) the base resin and (B) the polyrotaxane, at least one layerof the two or more inner cover layers may contain (A) the base resin and(B) the polyrotaxane. In this case, the outermost layer of the innercover layers preferably contains (A) the base resin and (B) thepolyrotaxane, and all layers of the inner cover layers may contain (A)the base resin and (B) the polyrotaxane.

The spherical core of the golf ball according to the present inventionpreferably has a diameter of 37.0 mm or more, more preferably 37.5 mm ormore, and even more preferably 38.0 mm or more, and preferably has adiameter of 42.2 mm or less, more preferably 41.8 mm or less, even morepreferably 41.5 mm or less, and most preferably 41.0 mm or less. If thediameter of the spherical core is 37.0 mm or more, the thickness of thecover does not become too thick and thus the resilience becomes better.On the other hand, if the diameter of the spherical core is 42.2 mm orless, the thickness of the cover does not become too thin and thus thecover functions better.

When the spherical core has a diameter in a range from 37.0 mm to 42.2mm, the compression deformation amount of the spherical core (shrinkingamount of the spherical core along the compression direction) whenapplying a load from 98 N as an initial load to 1275 N as a final loadto the spherical core is preferably 2.0 mm or more, more preferably 2.1mm or more, and even more preferably 2.2 mm or more, and is preferably5.0 mm or less, more preferably 4.9 mm or less, and even more preferably4.8 mm or less. If the compression deformation amount is 2.0 mm or more,the shot feeling becomes better, and if the compression deformationamount is 5.0 mm or less, the resilience becomes higher.

The thickness of the cover of the golf ball according to the presentinvention is preferably 0.5 mm or more, more preferably 0.7 mm or more,and even more preferably 0.9 mm or more, and is preferably 4.0 mm orless, more preferably 3.0 mm or less, and even more preferably 2.0 mm orless. This is because if the thickness of the cover falls within theabove range, lowering in the durability or abrasion resistance of thecover can be further suppressed. It is noted that when the cover has aplurality of layers, it is preferred that the total thickness of thecover layers falls within the above range.

In the case that the golf ball according to the present invention hastwo or more inner cover layers and the outermost cover layer, the totalthickness of the inner cover layers is preferably 0.5 mm or more, morepreferably 0.6 mm or more, and even more preferably 0.7 mm or more, andis preferably 4.0 mm or less, more preferably 3.5 mm or less, and evenmore preferably 3.0 mm or less. In addition, the thickness of each layerof the inner cover layers is preferably 0.3 mm or more, more preferably0.4 mm or more, and even more preferably 0.5 mm or more, and ispreferably 2.0 mm or less, more preferably 1.8 mm or less, and even morepreferably 1.6 mm or less.

The thickness of the outermost cover layer is preferably 4.0 mm or less,more preferably 3.0 mm or less, and even more preferably 2.0 mm or less,and is preferably 0.3 mm or more, more preferably 0.4 mm or more, andeven more preferably 0.5 mm or more. This is because if the thickness ofthe outermost cover layer falls within the above range, the obtainedgolf ball has better resilience or shot feeling.

The total number of the dimples formed on the cover is preferably 200 ormore and 500 or less. If the total number of the dimples is less than200, the dimple effect is hardly obtained. In addition, if the totalnumber of the dimples exceeds 500, the dimple effect is hardly obtainedbecause the size of the respective dimples is small. The shape (shape ina plan view) of the dimples includes, but is not limited to, a circle, apolygonal shape such as a roughly triangular shape, a roughlyquadrangular shape, a roughly pentagonal shape and a roughly hexagonalshape, and other irregular shape. The shape of the dimples may beemployed solely or at least two of them may be used in combination.

The golf ball according to the present invention preferably has adiameter in a range from 40 mm to 45 mm. In light of satisfying aregulation of US Golf Association (USGA), the diameter is particularlypreferably 42.67 mm or more. In light of prevention of air resistance,the diameter is more preferably 44 mm or less, and particularlypreferably 42.80 mm or less. In addition, the golf ball according to thepresent invention preferably has a mass in a range from 40 g to 50 g. Inlight of obtaining greater inertia, the mass is more preferably 44 g ormore, and particularly preferably 45.00 g or more. In light ofsatisfying a regulation of USGA, the mass is particularly preferably45.93 g or less.

When the golf ball according to the present invention has a diameter ina range from 40 mm to 45 mm, the compression deformation amount of thegolf ball (shrinking amount of the golf ball along the compressiondirection) when applying a load from 98 N as an initial load to 1275 Nas a final load to the golf ball is preferably 2.0 mm or more, morepreferably 2.4 mm or more, even more preferably 2.5 mm or more, and mostpreferably 2.8 mm or more, and is preferably 5.0 mm or less, morepreferably 4.5 mm or less. If the compression deformation amount is 2.0mm or more, the golf ball does not become too hard and thus the shotfeeling thereof becomes better. On the other hand, if the compressiondeformation amount is 5.0 mm or less, the resilience of the golf ballbecomes higher.

[Method for Producing Golf Ball]

The spherical core of the golf ball according to the present inventionmay be molded, for example, by heat pressing the spherical core rubbercomposition. The molding conditions for heat pressing the core rubbercomposition may be determined appropriately depending on the rubberformulation. Generally, the heat pressing is preferably carried out atthe temperature ranging from 130° C. to 200° C. for 10 to 60 minutes, orcarried out in a two-step heating of heating at the temperature rangingfrom 130° C. to 150° C. for 20 to 40 minutes followed by heating at thetemperature ranging from 160° C. to 180° C. for 5 to 15 minutes.

Examples of the method for molding the cover of the golf ball accordingto the present invention include a method which comprises molding thecover composition into a hollow shell, covering the core with aplurality of the hollow shells and subjecting the core with a pluralityof the hollow shells to the compression molding (preferably a methodwhich comprises molding the cover composition into a hollow half shell,covering the spherical core with two of the hollow half shells, andsubjecting the spherical core with two of the hollow half shells to thecompression molding); and a method which comprises injection molding thecover composition directly onto the spherical core. The cover of thegolf ball according to the present invention is preferably molded by theinjection molding method. This is because if the injection moldingmethod is adopted, the cover can be produced more easily.

When molding the cover in the compression molding method, molding of thehalf shell may be conducted by either a compression molding method or aninjection molding method, but the compression molding method ispreferred. The compression molding of the cover composition into thehalf shell can be carried out, for example, under a pressure of 1 MPa ormore and 20 MPa or less at a temperature of −20° C. or more and 70° C.or less relative to the flow beginning temperature of the covercomposition. By performing the molding under the above conditions, ahalf shell having a uniform thickness can be formed. Examples of themethod for molding the cover using half shells include a method ofcovering the spherical core with two of the half shells and thensubjecting the spherical core with two of the half shells to thecompression molding. The compression molding of the half shells into thecover can be carried out, for example, under a pressure of 0.5 MPa ormore and 25 MPa or less at a temperature of −20° C. or more and 70° C.or less relative to the flow beginning temperature of the covercomposition. By performing the molding under the above conditions, agolf ball cover having a uniform thickness can be formed.

In case of injection molding the cover composition into the cover, thecover composition extruded in a pellet form may be used for theinjection molding, or the cover materials such as the base resincomponents and the pigment may be dry blended, followed by directlyinjection molding the blended material. It is preferred to use upper andlower molds having a hemispherical cavity and pimples for forming thecover, wherein a part of the pimples also serves as a retractable holdpin. When molding the cover by the injection molding, for example, thehold pin is protruded to hold the core, and the cover composition ischarged and cooled to obtain the cover. For example, the molding of thecover may be conducted as follows: the cover composition heated to atemperature ranging from 200° C. to 250° C. is charged for 0.5 to 5seconds into a mold held under a pressure of 9 MPa to 15 MPa, and cooledfor 10 to 60 seconds, and the mold is opened to eject the golf ball.

In case of using an injection molding machine having an extruder and amold to mold the cover, the temperature at the cylinder (barrel) portionof the extruder (setting temperature of the extruder) is preferably 200°C. or more, more preferably 210° C. or more, and is preferably 270° C.or less, more preferably 260° C. or less. If the temperature at thecylinder (barrel) portion falls within the above range, the fluidity ofthe cover composition can be maintained.

The golf ball body having the cover formed thereon is ejected from themold, and is preferably subjected to surface treatments such asdeburring, cleaning and sandblast where necessary. In addition, ifdesired, a paint film or a mark may be formed. The paint film preferablyhas a thickness of, but is not particularly limited to, 5 μm or more,more preferably 7 μm or more, and preferably has a thickness of 50 μm orless, more preferably 40 μm or less, and even more preferably 30 μm orless. This is because if the thickness of the paint film is less than 5μm, the paint film is easy to wear off due to the continued use of thegolf ball, and if the thickness of the paint film exceeds 50 μm, thedimple effect is reduced and thus the flight performance of the golfball may be lowered.

FIG. 2 is a partially cutaway sectional view showing a golf ball 1according to an embodiment of the present invention. The golf ball 1comprises a spherical core 2, an inner cover layer 3 disposed outsidethe spherical core 2, and an outer cover layer 4 disposed outside theinner cover layer 3. A plurality of dimples 41 are formed on the surfaceof the outer cover layer 4. Other portion than the dimples 41 on thesurface of the outer cover layer 4 is lands 42. In a preferableembodiment of the present invention, the outer cover layer 4, the innercover layer 3, or both of the outer cover layer 4 and the inner coverlayer 3 contains (A) the base resin and (B) the polyrotaxane.

Examples

Next, the present invention will be described in detail by way ofexamples. However, the present invention is not limited to the examplesdescribed below. Various changes and modifications without departingfrom the spirit of the present invention are included in the scope ofthe present invention.

[Evaluation Methods] (1) Compression Deformation Amount (mm)

The deformation amount of the core along the compression direction(shrinking amount of the core along the compression direction), whenapplying a load from an initial load of 98 N to a final load of 1275 Nto the core, was measured.

(2) Material Hardness (Shore D Hardness)

Sheets with a thickness of about 2 mm were produced by injection molding(cylinder temperature: 230° C.) the base resin or the cover composition.The sheets were stored at 23° C. for two weeks. At least three of thesesheets were stacked on one another so as not to be affected by themeasuring substrate on which the sheets were placed, and the hardness ofthe stack was measured with an automatic hardness tester (Digitest II,available from Bareiss company) using a testing device of “Shore D”. Itis noted that when measuring the material hardness of the covercomposition, a composition obtained by blending predetermined materials((B) the polyrotaxane, titanium dioxide and so on) into (A) the baseresin is used for the measurement.

(3) Shot Feeling

An actual hitting test was carried out by using a driver by ten amateurgolfers (high skilled persons). In accordance with the following gradingstandard, the feeling of each golfer at hitting the golf ball wasevaluated. The shot feeling most evaluated by the ten golfers wasadopted as the shot feeling of that golf ball.

Grading Standard

G (Good): Impact is low and feeling is good.

F (Fair): Impact is normal.

P (Poor): Impact is great and feeling is bad.

(4) Coefficient of Restitution

A metal cylindrical object with a mass of 198.4 g was allowed to collidewith each golf ball at a speed of 40 m/sec, and the speeds of thecylindrical object and the golf ball before and after the collision weremeasured. Based on these speeds and the mass of each object, thecoefficient of restitution of each golf ball was calculated. Themeasurement was conducted using twelve samples for each golf ball, andthe average value thereof was adopted as the coefficient of restitutionfor that golf ball. It is noted that the coefficient of restitution ofthe golf ball No. 1 was defined as 100, and the coefficient ofrestitution of each golf ball was represented by converting thecoefficient of restitution of each golf ball into this index.

(5) Durability

A test was carried out by using an air gun to make each golf ballcollide with a metal plate at a speed of 45 m/sec for 100 times. Twelvesamples for each golf ball were used in the test. The durability of eachgolf ball was evaluated as follows: the durability of the golf ball wasevaluated as “G (Good)” if no damage occurred in all of the twelve golfballs, and the durability of the golf ball was evaluated as “P (Poor)”if damage occurred in some of the twelve golf balls.

(6) Abrasion Resistance

A commercially available sandwedge (XXIO 3 available from Dunlop SportsLimited) was installed on a swing robot available from GolfLaboratories, Inc., and each golf ball was hit at a head speed of 36m/sec. Each hit portion was observed, and the abrasion resistance wasevaluated according to the following three-level grading standard.

Grading Standard

G (Good): Almost no damage occurred on the surface of the golf ball.

F (Fair): The surface of the golf ball slightly abraded and fluffoccurred thereon.

P (Poor): The surface of the golf ball greatly abraded and remarkablyfluffed.

[Production of Golf Ball] (1) Production of Spherical Core

The rubber compositions having the formulations shown in Table 1 werekneaded, and heat pressed in upper and lower molds, each having ahemispherical cavity, to produce spherical cores. It is noted thatbarium sulfate was appropriately added such that the obtained golf ballhad a mass of 45.6 g.

TABLE 1 Rubber composition No. A B C D Formulation Polybutadiene rubber100 100 100 100 (parts by Zinc acrylate 27.5 27.5 31 32 mass) Zinc oxide5 10 5 5 Barium sulfate Appropriate Appropriate Appropriate Appropriateamount* amount* amount* amount*^(※) Dicumyl peroxide 0.9 0.9 0.7 0.9PBDS — 0.4 — — 2-Thionaphthol 0.1 0.1 — 0.1 Diphenyldisulfide — — 0.50.5 Zinc caprylate 2 — — — Benzoic acid — 2 — — Molding Moldingtemperature (° C.) 160 160 170 170 condition Molding time (min) 20 20 1520 Core diameter (mm) 39.4 39.4 38.2 39.8 Compression deformation amount(mm) 3.9 4.2 3.4 3.6 *As to the amount of barium sulfate, adjustment wasmade such that the golf ball had a mass of 45.6 g.

Polybutadiene rubber: “BR730 (high-cis polybutadiene)” available fromJSR Corporation

Zinc acrylate: “ZNDA-90S” available from Nisshoku Techno Fine ChemicalCo., Ltd.

Zinc oxide: “Ginrei (registered trademark) R” available from Toho ZincCo., Ltd.

Barium sulfate: “Barium Sulfate BD” available from Sakai ChemicalIndustry Co., Ltd.

Dicumyl peroxide: “PERCUMYL (registered trademark) D” available from NOFCorporation

PBDS: bis(pentabromophenyl) disulfide available from Kawaguchi ChemicalIndustry Co., Ltd.

2—Thionaphthol: available from Tokyo Chemical Industry Co., Ltd.

Diphenyldisulfide: available from Sumitomo Seika Chemicals Co., Ltd.

Zinc caprylate: available from Mitsuwa Chemicals Co., Ltd.

Benzoic acid: available from Tokyo Chemical Industry Co., Ltd.

(2) Production of Cover Layer (2-1) Production of Inner Cover Layer ofGolf Balls No. 1 to 12

The inner cover layer compositions were prepared by kneading thematerials having the formulations shown in Table 2 with a kneader. Theobtained inner cover layer composition was charged one by one into eachof the depressed part of the lower mold of the mold for molding halfshells, and a pressure was applied to mold the half shells. Thecompression molding was conducted under the conditions of a moldingtemperature of 170° C., a molding time of 5 minutes and a moldingpressure of 2.94 MPa. The spherical core obtained in the step (1) wasconcentrically covered with two of the obtained half shells, and thensubjected to compression molding to form the inner cover layer. Thecompression molding was conducted under the conditions of a moldingtemperature of 170° C. and a molding time of 15 minutes.

TABLE 2 Golf ball No. 1 2 3 4 5 6 7 8 Spherical Rubber composition No. AA A A B B B B core Diameter (mm) 39.4 39.4 39.4 39.4 39.4 39.4 39.4 39.4Inner Formulation: (A) Base Himilan AM7327 — 14 — — — 100 — — coverparts resin Himilan 1702 — — — — 45 — 36 45 layer by mass Himilan 155742.5 28.5 40.5 42.5 — — — — Himilan 1555 42.5 42.5 40.5 42.5 46 — 36 46Rabalon T3221C 15 15 19 15 9 — 28 9 (B) Polyrotaxane — — — 3 — — — 13 —Titanium oxide 4 4 4 4 4 4 4 4 Thickness (mm) 0.8 0.8 0.8 0.8 0.8 0.80.8 0.8 Material hardness of (A) base resin (Shore D) 52 50 50 52 55 4445 55 Material hardness of inner cover layer (Shore D) 52 50 50 50 55 4445 45 Outer Formulation: (A) Base Himilan AM7327 — — — — — — — — coverparts resin Himilan 1557 — — — — — — — — layer by mass Himilan 1555 1010 10 10 10 10 10 10 Himilan AM7337 5 5 5 5 5 5 5 5 Himilan AM7329 55 5555 55 55 55 55 55 Rabalon T3221C — — — — — — — — NUCREL N1050H 30 30 3030 30 30 30 30 (B) Polyrotaxane — — — — — — — — — Titanium oxide 3 3 3 33 3 3 3 JF-90 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Thickness (mm) 0.85 0.850.85 0.85 0.85 0.85 0.85 0.85 Material hardness of (A) base resin (ShoreD) 61 61 61 61 61 61 61 61 Material hardness of outer cover layer (ShoreD) 61 61 61 61 61 61 61 61 Ball Shot feeling F G G G F G G G propertyCoefficient of restitution 100 99 100 100 100 97 100 100 Durability G GP G G G P G Abrasion resistance G G G G G G G G Golf ball No. 9 10 11 1213 14 15 16 Spherical Rubber composition No. C C C C D D D D coreDiameter (mm) 38.2 38.2 38.2 38.2 39.8 39.8 39.8 39.8 Inner Formulation:(A) Base Himilan AM7327 — — — — — — — — cover parts resin Himilan 1702 —— — — — — — — layer by mass Himilan 1557 49 49 49 49 — — — — Himilan1555 49 49 49 49 — — — — Rabalon T3221C 2 2 2 2 — — — — (B) Polyrotaxane— — — — — — — — — Titanium oxide 4 4 4 4 — — — — Thickness (mm) 1.0 1.01.0 1.0 — — — — Material hardness of (A) base resin (Shore D) 60 60 6060 — — — — Material hardness of inner cover layer (Shore D) 60 60 60 60— — — — Outer Formulation: (A) Base Himilan AM7327 — 16 — — — 16 — —cover parts resin Himilan 1557 48 32 44 48 48 32 44 48 layer by massHimilan 1555 48 48 44 48 48 48 44 48 Himilan AM7337 — — — — — — — —Himilan AM7329 — — — — — — — — Rabalon T3221C 4 4 8 4 4 4 8 4 NUCRELN1050H — — — — — — — — (B) Polyrotaxane — — — 3 — — — 3 — Titanium oxide4 4 4 4 4 4 4 4 JF-90 — — — — — — — — Thickness (mm) 1.25 1.25 1.25 1.251.45 1.45 1.45 1.45 Material hardness of (A) base resin (Shore D) 58 5656 58 58 56 56 58 Material hardness of outer cover layer (Shore D) 58 5656 56 58 56 56 56 Ball Shot feeling P F F G P F F G property Coefficientof restitution 101 100 101 101 101 100 101 101 Durability G G G G G G GG Abrasion resistance G G F G G G F G

Himilan AM7327: Zinc ion-neutralized ethylene-methacrylic acid-butylacrylate ternary copolymer ionomer resin (melt flow rate (190° C., 2.16kgf): 3 g/10 min, bending stiffness: 35 MPa, material hardness: 44(Shore D)) available from Du Pont-Mitsui Polychemicals Co., Ltd.

Himilan 1702: Zinc ion-neutralized ethylene-methacrylic acid binarycopolymer ionomer resin (melt flow rate (190° C., 2.16 kgf): 16 g/10min, bending stiffness: 150 MPa, material hardness: 60 (Shore D))available from Du Pont-Mitsui Polychemicals Co., Ltd.

Himilan 1557: Zinc ion-neutralized ethylene-methacrylic acid binarycopolymer ionomer resin (melt flow rate (190° C., 2.16 kgf): 5 g/10 min,bending stiffness: 215 MPa, material hardness: 61 (Shore D)) availablefrom Du Pont-Mitsui Polychemicals Co., Ltd.

Himilan 1555: sodium ion-neutralized ethylene-methacrylic acid binarycopolymer ionomer resin (melt flow rate (190° C., 2.16 kgf): 10 g/10min, bending stiffness: 205 MPa, material hardness: 60 (Shore D))available from Du Pont-Mitsui Polychemicals Co., Ltd.

Himilan AM7337: sodium ion-neutralized ethylene-methacrylic acid binarycopolymer ionomer resin (melt flow rate (190° C., 2.16 kgf): 4 g/10 min,bending stiffness: 272 MPa, material hardness: 65 (Shore D)) availablefrom Du Pont-Mitsui Polychemicals Co., Ltd.

Himilan AM7329: Zinc ion-neutralized ethylene-methacrylic acid binarycopolymer ionomer resin (melt flow rate (190° C., 2.16 kgf): 5 g/10 min,bending stiffness: 221 MPa, material hardness: 64 (Shore D)) availablefrom Du Pont-Mitsui Polychemicals Co., Ltd.

Rabalon T3221C: styrene thermoplastic elastomer available fromMitsubishi Chemical Corporation

NUCREL N1050H: ethylene-methacrylic acid copolymer available from DuPont-Mitsui Polychemicals Co., Ltd.

Polyrotaxane: “SeRM (registered trademark) super polymer SH2400P (apolyrotaxane having a cyclodextrin with at least a part of hydroxylgroups thereof being modified with a caprolactone chain via —O—C₃H₆—O—group, polyethylene glycol as a linear molecule, and an adamantyl groupas a blocking group wherein the linear molecule has a molecular weightof 20,000, and the polyrotaxane has a hydroxyl value of 76 mg KOH/g anda total molecular weight of 400,000 in a weight average molecularweight)” available from Advanced Softmaterials Inc.

Titanium oxide: “A220” available from Ishihara Sangyo Kaisha, Ltd.

JF-90: bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate available fromJohoku Chemical Co. Ltd.

(2-2) Production of Outer Cover Layer of Golf Balls No. 1 to 16

The outer cover layer compositions in a pellet form were preparedrespectively by mixing the materials having the formulations shown inTable 2 with a twin-screw kneading extruder. The extruding conditionsfor the outer cover layer compositions were a screw diameter of 45 mm, ascrew rotational speed of 200 rpm and screw L/D=35, and the mixture washeated to 160° C. to 230° C. at the die position of the extruder.

When molding the outer cover layer, the hold pin was protruded to holdthe spherical body having the inner cover layer formed thereon, theouter cover layer composition heated to 260° C. was charged for 0.3second into a mold held under a pressure of 80 tons, and cooled for 30seconds, and the mold was opened to eject the golf ball. The surface ofthe obtained golf ball body was treated with sandblast and marked. Aclear paint was applied, and dried in an oven at 40° C. to obtain thegolf ball having a diameter of 42.7 mm and a mass of 45.6 g. For thegolf balls No. 13 to No. 16, no inner cover layer was formed, the outercover layer composition was injection molded directly onto the sphericalcore to produce the outer cover layer.

Evaluation results regarding the obtained golf balls are shown in Table2. The golf balls No. 4, 8, 12 and 16 are the golf balls comprising aspherical core and one or more cover layers disposed outside thespherical core wherein at least one layer of the cover layers contains:(A) a base resin containing (a-1) an ionomer resin and having a materialhardness of 58 or less in Shore D hardness; and (B) a polyrotaxanehaving a cyclodextrin with at least a part of hydroxyl groups thereofbeing modified with a caprolactone chain via —O—C₃H₆—O— group, a linearmolecule piercing through a cyclic structure of the cyclodextrin, andblocking groups located at both terminals of the linear molecule toprevent disassociation of the cyclodextrin. It is apparent from Table 2that the golf balls No. 4, 8, 12 and 16 have excellent shot feeling andresilience as well as improved durability and abrasion resistance.

The golf ball according to the present invention has excellent shotfeeling and resilience as well as improved durability and abrasionresistance.

This application is based on Japanese Patent Application No. 2016-253567filed on Dec. 27, 2016, the content of which is hereby incorporated byreference.

1. A golf ball comprising a spherical core and one or more cover layersdisposed outside the spherical core, wherein at least one layer of thecover layers contains: (A) a base resin containing (a-1) an ionomerresin and having a material hardness of 58 or less in Shore D hardness;and (B) a polyrotaxane having a cyclodextrin with at least a part ofhydroxyl groups of the cyclodextrin being modified with a caprolactonechain via —O—C₃H₆—O— group, a linear molecule piercing through a cyclicstructure of the cyclodextrin, and blocking groups located at bothterminals of the linear molecule to prevent disassociation of thecyclodextrin.
 2. The golf ball according to claim 1, wherein (A) thebase resin further contains (a-2) a non-ionomer resin.
 3. The golf ballaccording to claim 1, wherein (B) the polyrotaxane has polyethyleneglycol as the linear molecule and an adamantyl group as the blockinggroup.
 4. The golf ball according to claim 1, wherein the cover layercontaining (A) the base resin and (B) the polyrotaxane contains (B) thepolyrotaxane in an amount of from 0.1 part by mass to 20 parts by masswith respect to 100 parts by mass of (A) the base resin.
 5. The golfball according to claim 1, wherein the cover layer containing (A) thebase resin and (B) the polyrotaxane has a material hardness of from 40to 58 in Shore D hardness.
 6. The golf ball according to claim 1,wherein (A) the base resin contains (a-1) the ionomer resin in an amountof 50 mass % or more.
 7. The golf ball according to claim 2, wherein (A)the base resin contains (a-2) the non-ionomer resin in an amount of from1 mass % to 50 mass %.
 8. The golf ball according to claim 2, wherein amass ratio ((a-2)/(a-1)) of (a-2) the non-ionomer resin to (a-1) theionomer resin in (A) the base resin ranges from 1/99 to 50/50.
 9. Thegolf ball according to claim 2, wherein (a-2) the non-ionomer resin isat least one member selected from the group consisting of a polyamide, astyrene elastomer, a polyolefin elastomer, a polyamide elastomer, apolyester elastomer, a binary copolymer composed of an olefin and anα,β-unsaturated carboxylic acid having 3 to 8 carbon atoms, and aternary copolymer composed of an olefin, an α,β-unsaturated carboxylicacid having 3 to 8 carbon atoms and an α,β-unsaturated carboxylic acidester.
 10. The golf ball according to claim 1, wherein a total ratio of(A) the base resin and (B) the polyrotaxane to all the resin componentsin the cover layer containing (A) the base resin and (B) thepolyrotaxane is 60 mass % or more.
 11. The golf ball according to claim1, wherein (a-1) the ionomer resin is at least one member selected fromthe group consisting of an ionomer resin consisting of a metalion-neutralized product of a binary copolymer composed of an olefin andan α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms; and anionomer resin consisting of a metal ion-neutralized product of a ternarycopolymer composed of an olefin, an α,β-unsaturated carboxylic acidhaving 3 to 8 carbon atoms and an α,β-unsaturated carboxylic acid ester.12. The golf ball according to claim 1, wherein (A) the base resin hasthe material hardness of 42 or more in Shore D hardness.
 13. The golfball according to claim 1, wherein (B) the polyrotaxane has a hydroxylvalue of from 10 mg KOH/g to 400 mg KOH/g.
 14. The golf ball accordingto claim 1, wherein (B) the polyrotaxane has a total molecular weight offrom 30,000 to 3,000,000 in a weight average molecular weight.
 15. Agolf ball comprising a spherical core and one or more cover layersdisposed outside the spherical core, wherein at least one layer of thecover layers contains: (A) a base resin having a material hardness of 58or less in Shore D hardness and containing (a-1) an ionomer resin and(a-2) a non-ionomer resin in a mass ratio ((a-2)/(a-1)) of (a-2) thenon-ionomer resin to (a-1) the ionomer resin ranging from 1/99 to 50/50;and (B) a polyrotaxane having a cyclodextrin with at least a part ofhydroxyl groups of the cyclodextrin being modified with a caprolactonechain via —O—C₃H₆—O— group, a linear molecule piercing through a cyclicstructure of the cyclodextrin, and blocking groups located at bothterminals of the linear molecule to prevent disassociation of thecyclodextrin, and wherein the cover layer containing (A) the base resinand (B) the polyrotaxane contains (B) the polyrotaxane in an amount offrom 0.1 part by mass to 20 parts by mass with respect to 100 parts bymass of (A) the base resin.
 16. The golf ball according to claim 15,wherein (a-2) the non-ionomer resin is at least one member selected fromthe group consisting of a polyamide, a styrene elastomer, a polyolefinelastomer, a polyamide elastomer, a polyester elastomer, a binarycopolymer composed of an olefin and an α,β-unsaturated carboxylic acidhaving 3 to 8 carbon atoms, and a ternary copolymer composed of anolefin, an α,β-unsaturated carboxylic acid having 3 to 8 carbon atomsand an α,β-unsaturated carboxylic acid ester.
 17. The golf ballaccording to claim 16, wherein (B) the polyrotaxane has a totalmolecular weight of from 30,000 to 3,000,000 in a weight averagemolecular weight.
 18. The golf ball according to claim 17, wherein (B)the polyrotaxane has a hydroxyl value of from 10 mg KOH/g to 400 mgKOH/g.
 19. The golf ball according to claim 18, wherein (B) thepolyrotaxane has polyethylene glycol as the linear molecule and anadamantyl group as the blocking group.